U.S. Pat. No. 5,040,169 teaches an optical coupling system in which system nodes are connected to one another through the medium of an input interface, a central coupling device and an output interface. The data information transmitted between the nodes is modulated on different carrier waves or wavelength channels. The signals that are sent between the nodes will thus include a number of wavelength channels, for instance W1, W2, W3, W4, in accordance with one embodiment of the patent. The signals are fed to the inputs of the coupling device via the input interface, wherein the wavelength channels are switched, or in other words cross-connected, in the coupling device in accordance with a fixed cross-connection schedule. The cross-connection schedule discloses to which output a certain wavelength channel will be connected when said channel is fed-in on a certain input. Thus, correct selection of a wavelength channel in accordance with the cross-connection schedule will enable any two nodes in the system to be connected together.
According to the method described in the aforesaid patent specification, actual cross-connection is achieved by dividing the wavelength channels applied to an input of the coupling device into two branches in a first branch point, wherein half of the wavelength channels are connected to the first branch and the other half of said channels are connected to the second branch. This division of the wavelength channels is repeated in further branch points, until only one wavelength channel remains on each branch. The branches are disposed in "horizontal planes", one horizontal plane for each input of the coupling device. The wavelength channels are then re-combined in "vertical planes". Thus, two wavelength channels are joined together in a first combination point, and these two wavelength channels are joined to two other wavelength channels in a second combination point, and so on, until a signal is delivered from the coupling device. The number of wavelength channels in the output signal will then equal the number of wavelength channels in the input signal applied to the input of the coupling device. The coupling device operates in accordance with the principle of complete division of the wavelength channels of the input signals, whereafter the output signals are obtained by combining wavelength channels from all input signals.
The drawback with the known coupling device resides in its complex construction which requires a large number of components.